linux-kernel - Re: [PATCH] spi: Increase imx51 ecspi burst length based on transfer length

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Date:   Fri, 15 Sep 2023 00:47:49 +0200
From:   Sebastian Reichel <sre@...nel.org>
To:     Stefan Moring <stefan.moring@...hnolution.nl>
Cc:     broonie@...nel.org, shawnguo@...nel.org, s.hauer@...gutronix.de,
        festevam@...il.com, linux-imx@....com, linux-spi@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] spi: Increase imx51 ecspi burst length based on transfer
 length

Hi,

On Wed, Jun 28, 2023 at 02:54:06PM +0200, Stefan Moring wrote:
> IMX51 supports 4096 bit burst lengths. Using the spi transfer length
> instead of bits_per_word increases performance significantly.
> 
> Signed-off-by: Stefan Moring <stefan.moring@...hnolution.nl>
> ---

I have an i.MX6ULL system with "inanbo,t28cp45tn89-v17" panel, which
breaks due to this change. Reverting this patch results in working
panel. Note, that the panel driver [0] does 'spi->bits_per_word = 9;'.

[0] drivers/gpu/drm/panel/panel-sitronix-st7789v.c

-- Sebastian

>  drivers/spi/spi-imx.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c
> index 34e5f81ec431..cbd306c25d28 100644
> --- a/drivers/spi/spi-imx.c
> +++ b/drivers/spi/spi-imx.c
> @@ -644,9 +644,13 @@ static int mx51_ecspi_prepare_transfer(struct spi_imx_data *spi_imx,
>  	if (spi_imx->slave_mode && is_imx53_ecspi(spi_imx))
>  		ctrl |= (spi_imx->slave_burst * 8 - 1)
>  			<< MX51_ECSPI_CTRL_BL_OFFSET;
> -	else
> -		ctrl |= (spi_imx->bits_per_word - 1)
> -			<< MX51_ECSPI_CTRL_BL_OFFSET;
> +	else {
> +		if (spi_imx->count >= 512)
> +			ctrl |= 0xFFF << MX51_ECSPI_CTRL_BL_OFFSET;
> +		else
> +			ctrl |= (spi_imx->count*8 - 1)
> +				<< MX51_ECSPI_CTRL_BL_OFFSET;
> +	}
>  
>  	/* set clock speed */
>  	ctrl &= ~(0xf << MX51_ECSPI_CTRL_POSTDIV_OFFSET |
> @@ -1243,6 +1247,7 @@ static int spi_imx_setupxfer(struct spi_device *spi,
>  		spi_imx->spi_bus_clk = t->speed_hz;
>  
>  	spi_imx->bits_per_word = t->bits_per_word;
> +	spi_imx->count = t->len;
>  
>  	/*
>  	 * Initialize the functions for transfer. To transfer non byte-aligned
> -- 
> 2.34.1
> 

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